A pork producer's profit depends on the cost of feed and the market price for pork, and on the ability to attain a high percentage of live births and pigs weaned per litter. Furthermore, a pork producer's profit is contingent on controlling the cost of personnel used to assist in the farrowing operation. Thus, any significant technological advance useful in optimizing efficiency and reducing personnel costs may receive wide acceptance among pork producers.
Having experienced and skilled personnel available to assist during farrowing and the neonatal period is important for several reasons. When giving birth to large litters a sow will often tire. This results in the stillbirth of the last few pigs of the litter who are unable to escape the uterus and reach air before suffocating. Further, pigs are born without hair and, as such, are susceptible to temperature changes. Hypothermia can often cause the death of young pigs.
It should also be appreciated that the litter may be larger than the number of functional nipples available on the sow. Nipples on the upper chest are also typically more productive than those at the sow's hindquarter. Thus, small pigs that cannot compete with their litter mates may be pushed to the less productive nipples and not receive the nutrients needed to grow or even survive. Specifically, since pigs receive their immunity to disease through the milk of the sow, undernourished pigs are very susceptible to diseases and infections. Further, weakened pigs may be slowed and unable to move quickly enough to avoid being accidentally crushed by the sow in the pen.
With proper care, the rate of pig survival can be greatly increased. The assisting personnel can help the sow as she farrows thereby helping her when she tires and reducing the number of stillborns. Obstructions such as mucous may be cleaned from the nostrils of newborn pigs to reduce stress and/or even prevent suffocation. Since sows are receptive to pigs born of another sow, cross-fostering of pigs can be practiced. By proportioning the number of pigs per sow and placing pigs of approximately the same size with the same sow, better overall nutrition of all the newborn pigs is assured.
Maintaining a high birth rate in a herd of swine and using personnel efficiently so as to minimize costs has lead pork producers to seek methods for synchronizing farrowing. In the past, pork producers have sought to synchronize farrowing among the sows of a herd so as to reduce the man-hours required to provide care and increase newborn pig survival.
Synchronized weanings have been used in an effort to synchronize subsequent farrowings. Specifically, after the sows have all been nursing present litters for about three weeks, the litters are weaned. Four to six days after weaning, the sows are again ready for breeding. By breeding all the sows on or about the same day, farrowings can be synchronized to fall within a relatively short period. While this technique is more efficient than random breeding, biological variations in the sows of the herd may result in farrowing taking place over as much as a seven day period. Also, farrowing can occur at any time of the day or night.
Another means of synchronizing farrowing in swine herds has been via the use of various veterinary pharmaceuticals. However, the extreme potency of some of the drugs employed for uterine stimulation can cause injury to the sows uterus during delivery. Steroids such as progesterone or "progestin" may be administered to sows late in the gestation period so as to extend gestation and delay farrowing. However, the utilization of progesterone to delay farrowing has been shown to increase the rate of stillbirths and incidents of dystocia or abnormal labor.
Prostaglandin F.sub.2.alpha. (PGF.sub.2.alpha.), or its analogs, e.g., cloprostenol, may also be administered to sows so as to induce parturition or farrowing. The use of prostaglandins to synchronize farrowing in a herd is, however, of limited effectiveness. The average time for responding to PGF.sub.2.alpha. or cloprostenol treatment is 33 hours, with a range of 15-48 hours (L. Hermansson et at., Nord. Vet. Med., 33, 349-353 (1981)). This response variation is too great to allow for the potential benefits of farrowing induction.
Recently, oxytocin was used in combination with PGF.sub.2.alpha. or its analog to facilitate induction of farrowing (P. Chantaraprateep et at., Aust. Vet. J., 63, 254-256 (1986); and G. D. Dial et al., Am. J. Vet. Res., 48, 966-970 (1987)). However, this approach is not satisfactory because the procedure is not practical. It results in highly variable onset of the induced farrowing or potential loss of piglets resulting from dystocia induced by these drugs.
The combination of PGF.sub.2.alpha. and xylazine to induce farrowing has also been studied (J. C. H. Ko et al., Theriogenology, 31, 795-800 (1989)). This study clearly indicates that this combination could be used to reliably and effectively synchronize farrowing. Xylazine is an .alpha..sub.2 -adrenergic agonist, and .alpha..sub.2 -agonists are potent myometrial contractants in pigs. These drugs offer an alternative to oxytocin for the stimulation of myometrial contraction. In addition, their effects on the myometrium can be reversed by .alpha..sub.2 -adrenergic antagonists, unlike the effects oxytocin. However, xylazine's sedative effect may not be desirable when used as an oxytocic agent. Thus, a need exists for a safe and effective method for synchronizing farrowing in pregnant sows, particularly without sedative effects.